Fluid thrusters for use in marine applications conventionally comprise external propellers, or jet propulsion where water passes into an internal impeller. External propellers are well-known, have a number of problems including efficiency, and problems with wake.
Impellers, such as used in jet boats, consist of an internal flow tube having a forward inlet through which water passes. The impeller rotates at high speed in the flow tube and propels the water through the flow tube and to the outlet. An advantage of the jet propulsion thrusters is that there is little likelihood of propeller damage in shallow water.